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Influence of the mass flow rate and void fraction on the vibration of a horizontal U-bend subjected to an upwards flowing air/water-mixture
Laurent De Moerloose, Jan Vierendeels, Joris Degroote

Last modified: 2018-06-25


U-bends are a common geometry in heat exchangers. In this paper, a U-bend is considered with horizontal straight pipes subjected to an initially stratified water/air flow which moves upwards against gravity. The flow is analyzed with a Reynolds-Averaged Navier-Stokes Volume-Of-Fluid approach. For low mass flow rates, liquid slugs are naturally formed at the entrance of the bend. The transient force on the tube allows to determine precisely the moments of slug initiation and thus to quantify the slug frequency. Firstly, the tube is assumed to be rigid and the dependence of the initiation point of the slugs and the slug frequency on the inlet conditions is investigated. It is also shown that the slug initiation point does not depend on the liquid viscosity, even though the water-air interface is more unstable with increased liquid viscosity. Secondly, a Fluid-Structure Interaction calculation is applied in order to determine the vibration amplitude of the tube. The influence of the mass flow rate and the inlet void fraction on the vibration amplitude and frequency is investigated. The aim is to detect the flow regime and void fraction directly from vibration characteristics.


computational fluid dynamics, fluid-structure interaction, multiphase flow, U-bend

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